powerpc: Finally remove unnecessary headers from asm/prom.h

Remove all headers included from asm/prom.h which are not used
by asm/prom.h itself.

Declare struct device_node and struct property locally to
avoid including of.h

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/4be954abef978b34cff9193fc566ffefdd3517bb.1657264228.git.christophe.leroy@csgroup.eu

arch/powerpc/include/asm/prom.h

@@ -12,16 +12,10 @@
  * Updates for PPC64 by Peter Bergner & David Engebretsen, IBM Corp.
  */
 #include <linux/types.h>
-#include <asm/irq.h>
-#include <linux/atomic.h>
 #include <asm/firmware.h>
 
-/* These includes should be removed once implicit includes are cleaned up. */
-#include <linux/of.h>
-#include <linux/of_fdt.h>
-#include <linux/of_address.h>
-#include <linux/of_irq.h>
-#include <linux/platform_device.h>
+struct device_node;
+struct property;
 
 #define OF_DT_BEGIN_NODE	0x1		/* Start of node, full name */
 #define OF_DT_END_NODE		0x2		/* End node */